Introducer sheath with electrodes for use in bleed detection

ABSTRACT

An introducer includes a sheath for introducing a catheter into a blood vessel at an insertion site and a plurality of electrodes on the sheath. The introducer also includes an impedance assessment unit connected to the electrodes. The impedance assessment unit includes a power source and a wireless transceiver and is configured to inject one of a predetermined current or voltage across a first pair of electrodes and to measure the other of the current or voltage across a second pair of electrodes. The impedance assessment unit also is configured to perform at least one: wirelessly transmit current and voltage values to an external apparatus for detection of a bleed, and compute an impedance based on the current and voltage and wirelessly transmit the computed impedance to the external apparatus for detection of the bleed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application claiming priority to U.S.patent application Ser. No. 13/468,774, filed May 10, 2012, titled“Introducer Sheath With Electrodes,” which is a continuation-in-partapplication claiming priority to U.S. patent application Ser. No.12/581,101, filed Oct. 16, 2009, titled “Introducer Sheath withElectrodes,” Ser. No. 12/348,658, filed Jan. 5, 2009, titled “IntroducerSheath With Electrodes,” and Ser. No. 12/348,695, filed Jan. 5, 2009,titled “Catheter with Electrodes for Impedance and/or ConductionVelocity Measurement.” Through application Ser. No. 12/348,695, thepresent application also claims priority to provisional application Ser.No. 61/019,131, filed Jan. 4, 2008, and titled “Method, System, andDevice for Detection of Pericardial Blood or Fluid.” All cases listedabove are incorporated herein by reference.

BACKGROUND

1. Field of the Disclosure

This invention relates generally to the field of medical devices. Morespecifically, the invention relates to a method and device usingimpedance for the detection of fluid (e.g., blood) bleeding such aspericardial effusion, retroperitoneal effusion, etc.

2. Background Information

Radiofrequency ablation (RF ablation) or other invasive cardiacprocedures which involve operation within the cardiac chambers, coronaryarteries or the heart's venous anatomy have saved many lives. Theseprocedures often involve percutaneous access into the cardiac chambersor epicardial arterial or venous vessels. Catheter, pacing lead, sheath,or other types of device manipulations frequently are performed as keyparts of these procedures. Example of this include balloon angioplastyor stent placement. Often, catheter access to the femoral artery isneeded to enable access to the heart of elsewhere in the body.

A rare but potentially dangerous complication of these and similarprocedures is inadvertent perforation of a cardiac chamber or anepicardial vessel. Retroperitoneal bleeding, arteriovenous fistula,pseudoaneurysms, and hematoma formation is also possible at the site ofthe insertion of the catheter into the femoral or other artery or vein.Perforations of a cardiac chamber or an epicardial vessel may lead toaccumulation of blood (or other fluids) in the pericardial space or sac.This condition is referred to pericardial effusion. Cardiac tamponade isthe patho-physiologic state wherein accumulation of blood or other fluidin the pericardial space or sac leads to impaired filling of the heartand a secondary decrease in cardiac output and consequential hemodynamicderangement. It is not unusual in clinical procedures for the onset ofperforation to be heralded by the onset of hemodynamic derangements suchas drop in blood pressure. In such cases it is frequently only at thattime that the presence of a perforation is recognized. Much time mayhave elapsed between the creation of a perforation and the subsequentaccumulation of enough blood or fluid to create ahemodynamically-significant pericardial effusion or tamponade. Ofcritical clinical significance is that early detection of suchperforation may allow the operator to implement interventions (forexample discontinuation of peri-operative anticoagulation) that wouldmitigate the untoward consequences of pericardial effusion.

Retroperitoneal bleeding, arteriovenous fistulae, or hematomas may leadto hemotoma formation, pain, blood loss, shock, or death. Its detectionis frequently only noted after hypotension or other symptoms are noted.There may be no other signs associated with bleeding. As in the case ofa pericardial effusion prompt recognition offers the opportunity forpotentially lifesaving intervention. Another frequent complication ofsuch procedures involves development of blood clots (“thrombosis”)within the body of the sheath. These clots may travel (“embolize”) viathe circulation and lead to necrosis or ischemia of tissue subserved bythese blood vessels.

It follows that a method and device which could more rapidly detect thepresence of pericardial or retroperitoneal bleeding, aretriovenousfistula, or hematoma, prior to the onset of symptoms, is highlydesirable. Rapid detection of such bleeding or fluid accumulation canlead to more timely management—such as aborting the procedure orreversal of the patient's anticoagulation response during such cardiacprocedures.

BRIEF SUMMARY

In accordance with at least one embodiment, an introducer includes asheath for introducing a catheter into a blood vessel at an insertionsite and a plurality of electrodes on the sheath. The introducer alsoincludes an impedance assessment unit connected to the electrodes. Theimpedance assessment unit includes a power source and a wirelesstransceiver and is configured to inject one of a predetermined currentor voltage across a first pair of electrodes and to measure the other ofthe current or voltage across a second pair of electrodes. The impedanceassessment unit also is configured to perform at least one: wirelesslytransmit current and voltage values to an external apparatus fordetection of a bleed, and compute an impedance based on the current andvoltage and wirelessly transmit the computed impedance to the externalapparatus for detection of the bleed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an introducer sheath with an electrode usable to determineimpedance for the detection of bleeding in accordance with variousembodiments.

FIG. 2 shows a view of the sheath in cross-section with a partial ringelectrode on an exterior surface in accordance with various embodiments.

FIG. 3 shows a view of the sheath in cross-section with a complete ringelectrode on the exterior surface in accordance with variousembodiments.

FIG. 4 shows a view of the sheath in cross-section with an electrodeembedded in the material of the sheath. in accordance with variousembodiments.

FIG. 5 shows a view of the sheath in cross-section with an electrode onan interior surface of the sheath in accordance with variousembodiments.

FIG. 6 depicts the sheath inserted into a blood vessel of person andconnected to an impedance measuring apparatus in accordance with variousembodiments.

FIG. 7 shows a method in accordance with various embodiments.

FIG. 8 shows an impedance measuring apparatus in accordance with variousembodiments.

FIG. 9 illustrates various impedance thresholds stored in the impedancemeasuring apparatus.

FIG. 10 depicts an illustrative method of calibrating the impedancemeasuring apparatus.

FIG. 11 shows an introducer containing an impedance assessment unit inaccordance with various embodiments.

FIG. 12 shows a block diagram of the introducer of FIG. 11 in accordancewith various embodiments.

FIG. 13 illustrates use of the introducer of FIG. 11 in accordance withvarious embodiments.

NOTATION AND NOMENCLATURE

In the following discussion and in the claims, the term “fluid” isdefined to include blood and other types of body fluids or gases thatmay bleed or leak from a vessel or organ. All references to an impedancemeasurement being made encompasses any of the variations describedherein as performed by the combination of the impedance assessment unitand an external apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with preferred embodiments of the invention, a system andmethod are disclosed herein that involves real-time assessment ofresistance or impedance to an electrical signal (current or voltage).Accumulation of sufficient fluid or blood in such areas as thepericardial space leads to changes in both the direct current (DC)resistance and/or the complex impedance to alternating current (AC)current flow. A change in either the resistance or the complex impedancesignals fluid accumulation in the space through which the electricalcurrent travels. Embodiments of the invention also use conduction timebetween two vectors as another variable which may be analyzed. Variousembodiments are described herein for measuring impedance to detect fluidbleeding. Impedance may be computed by injecting a known current (DC orAC) and measuring the resulting voltage, or imposing a known voltageacross the electrodes and measuring the resulting current. The ratio ofvoltage to current determines impedance.

In accordance with one such embodiment, FIG. 1 illustrates an introducer10 usable to insert a catheter into a blood vessel (vein or artery). Theintroducer comprises a hollow sheath 12 having a distal end 19 that isinsertable into a blood vessel of a person. The blood vessel may be anartery or a vein. In at least one application, the blood vessel is thefemoral artery, but other blood vessels may be used as well. In theillustrative embodiment of FIG. 1, multiple electrodes 20 a, 20 b, 20 c,and 20 d are provided on the sheath 12. Such electrodes can be providedat any of a variety of locations along the sheath 12. As will beexplained below, the electrodes are usable to measure impedance of theperson so as to detect bleeding (e.g., retroperitoneal bleeding).

Impedance between pairs of electrodes within the sheath can also bemeasured to assess the presence of such phenomenona as clots within thesheath. In this embodiment, the system can be based on using only onepair of electrodes such that the injected current and the detectedvoltage are from one pair of electrodes, or on multiple pairs ofelectrodes such that the injected current and the detected voltage aretwo separate pairs of electrodes. For example, one pair of electrodes isused to inject current and another pair of electrodes is used to measurethe resulting voltage to thereby assess impedance, or vice versa (aknown voltage is imposed on pair of electrodes and current is measured).Although two different pairs of electrodes are used, an electrode may becommon to both pairs. Other configurations utilizing multiple electrodesare also feasible embodiments.

The sheath 12 may be coupled to a hub 15 which may incorporate ahemostasis valve 21 from which a side arm 14 may extend that allows thesheath to be used to administer fluids and or drugs. A valve 16 isprovided on the opposing end of the side arm 14. The introducer 10 alsoincludes a dilator 28 that is insertable into the hollow sheath 12. Thedilator and sheath function to permit a catheter to be inserted into theblood vessel. Independently from the preceding features, the sheath 12may also include other features to facilitate simple “peel-away” removalwithout disturbing a catheter having been passed the lumen of the sheath12. Referring still to FIG. 1, electrical conductors 17 (e.g., wires)extend along at least part of the sheath 12 from the electrodes 20 a-dand can be connected to an external device (i.e., a device external tothe person/patient that receives the sheath 12). The conductors 17preferably include at least one insulated conductor for each electrode20. The conductors 17 are usable to conduct signals between at least oneelectrode 20 on the sheath and the external device for impedancemeasurements.

In FIG. 1, four electrodes 20 are shown on the sheath 12, but in otherembodiments, more or less than four electrodes may be provided on thesheath. Alternately only one electrode may be present on the sheath,with another electrode used in the impedance measurements being locatedapart from the sheath (e.g., an external electrode as illustrated inFIG. 6). Impedances between any individual pair electrodes may bemeasured.

FIGS. 2-5 illustrate various embodiments of the electrodes 20 a-d. Eachfigure shows a view of the sheath facing distal end 19. Referring firstto FIG. 2, sheath 12 comprises material 24 formed as a tubular memberand comprising an inner surface 23 and an outer surface 25. In FIG. 1,the electrode 20 comprises a partial ring electrode disposed about aportion of the perimeter of the outer surface 25. In some embodiments,the electrode 20 is adhered (e.g. via glue) to the outer surface 25. Inother embodiments, the electrode 20 covers more than 50% of theperimeter of the outer surface 25 and is retained (e.g., clamped) inplace like a bracelet.

FIG. 3 illustrates an embodiment of the electrode 20 in which theelectrode is a complete ring electrode (i.e., completely surrounds theouter surface 25 of the sheath 12).

In FIGS. 2 and 3, the electrode 20 is provided on the outer surface 25of the sheath. In FIG. 4, the electrode 20 is embedded within thematerial 24 of the sheath in which case the sheath materials (or atleast the segments of the sheath material between the electrodes) mustbe conductive of electrical signals in the range employed. Furthermore,for the purposes of detection of clot, impedance or conduction (fordetecting bleeding) between these electrodes may be measured. In FIG. 5,the electrode 20 is provided on the inner surface 23 of the sheath andthus within the inner hollow portion of the sheath.

In some embodiments, the electrode 20 is located on the sheath so thatthe electrode will be inside the blood vessel once the sheath isinserted into the vessel. In other embodiments, the electrode may beprovided on the sheath at the proximal end outside the blood vessel (andperhaps even outside the person's body). In such embodiments, theelectrode 20 preferably is provided on the inner surface of the sheath(similar to that shown in FIG. 5). Normally, the sheath is filled withbody fluid (e.g., blood).

FIG. 6 illustrates a person lying supine with the sheath 12 insertedinto a blood vessel 29. The conductors 17 from the electrodes 20 areconnected to an impedance measuring apparatus 35. The impedancemeasuring apparatus 35 comprises a current source 36 and logic 38. Thecurrent source 36 may be part of the logic 38 if desired. One or moreadditional electrodes 30 is also connected to the impedance measuringapparatus 35. Such an additional electrode is also herein referred to asthe non-sheath electrode or the non-sheath electrodes. The currentsource 36 injects an electrical current through one of the electrodes 20or 30. The current then passes through the person's tissues, into theother electrode and back to the current source. The injected current maycomprise a series of pulses or a sustained current. The amplitude of thecurrent may be in the sub-physiological range such as 1 milliamp. If apulse train is used, the pulse width may be 0.2 milliseconds or less andhave a frequency of between 5,000 and 500,000 Hz or higher.

The current source 36 or logic 38 measures the voltage across theelectrodes 20, 30 resulting from the current, and computes the ratio ofthe voltage to current to compute impedance. The impedance is altered inthe presence of bleeding and thus can be correlated to bleeding such asretroperitoneal bleeding. The device may also calculate the conductiontime between the electrodes. Bleeding will also alter the conductiontime between tissues. Alternatively, rather than a current source, avoltage source can be used to impose a specified voltage on theelectrodes 20, 30 and the resulting current level is measured to computeimpedance.

The non-sheath electrodes 30 may be located at any of a variety oflocations. The illustrative embodiment of FIG. 6 shows the non-sheathelectrode 30 attached to the skin on the person's back as a patchelectrode. In other embodiments for detecting retroperitoneal bleeding,the non-sheath electrode 30 can be attached to a urinary catheter, arectal temperature probe, an electrosurgical grounding pad, or a patchon a lateral aspect of the back as desired, separately or incombination.

In accordance with at least some embodiments, the sheath 12 may comprisetwo or more electrodes 20. Another pair of electrodes may be attached tothe patient's skin (e.g. back, abdomen) as noted above. One paircomprising one of the sheath electrodes and one of the skin electrodesis used to inject current and the other pair of electrodes (i.e., theother sheath electrode and skin electrode) is used to measure theresulting voltage for the impedance computation.

In another embodiment, the sheath 12 may include four electrodes asshown in FIG. 1. Two electrodes are placed distally near the distal tip19 and two are placed proximally of the shaft of the sheath. A currentis sent through one distal electrode, through the patient's body to oneof the proximal electrodes (the direction of current flow can be in theopposite direction as well). The remaining pair of electrodes measuresthe voltage for the impedance computation.

In some embodiments, each possible pair of electrodes is used tosend/receive current with the remaining electrodes used to measurevoltage for an impedance computation.

In some embodiments, each possible pair of electrodes is used tosend/receive current with the remaining electrodes used to measurevoltage for an impedance calculation. The system may cycle through eachsuch electrode pair combination.

In yet other embodiments, the sheath may not have any electrodes.Instead, multiple electrodes (e.g., 5 or more) are placed on thepatient's abdomen near the tip of electrode-less sheath. As before, eachpossible electrode combination is cycled through the process of sendingthe current, conducting the current, measuring the voltage, andcomputing the impedance.

FIG. 7 shows an illustrative method. At 102, an electrode is coupled tothe person. In the embodiments of FIGS. 1-6, one or more electrodes arelocated on an introducer sheath 12 and coupled to a person as the sheathis inserted into a blood vessel. At 104, one or more non-sheathelectrodes are also coupled to the person (e.g., back electrode 30 asshown in FIG. 6). At 106, upon a user activating a control on theimpedance measuring device to begin the impedance measuring activity,the impedance measuring apparatus 35 injects current and, at 108,computes the impedance (e.g., measures the voltage and computes theratio of voltage to current).

At 110, the impedance measuring apparatus 35 determines if the impedanceis indicative of bleeding. In some embodiments, the logic 38 of theimpedance (or conduction time) measuring apparatus 35 compares thecomputed impedance to a predetermined threshold, derived threshold basedon baseline measurements at the onset of the procedure, otherwisedefined acceptable range. The logic 38 determines that bleeding hasoccurred if the computed impedance or conduction time is outside of theacceptable range for the threshold as previously defined. If bleedinghas been detected, the logic 38 may alert a user via an audible and/orvisual indicator.

In some embodiments, the impedance measuring apparatus 35 injects aknown current and measures the resulting voltage to determine impedance.In other embodiments, the impedance measuring apparatus 35 applies aknown voltage to the electrodes and measures the resulting current todetermine impedance.

It may be desirable to leave the sheath 12 in place in the person'sblood vessel following the completion of the medical procedure (e.g., RFablation) for which the sheath was used in the first place. It ispossible that bleeding (e.g., retroperitoneal bleeding) will begin afterthe completion of the medical procedure. With the sheath 12 still inplace, impedance measurements can be made via the impedance measuringapparatus 35 to detect post-medical procedure completion onset ofbleeding. A user of the impedance measuring apparatus can activate acontrol (e.g., press a button) on the impedance measuring apparatus toactivate an impedance/bleed monitoring.

Besides retroperitoneal bleeding, arteriovenous fistulae, or hematomas,other types of internal bleeding may occur as well. For example, duringa catheterization procedure of a patient's heart or surrounding bloodvessel(s), bleeding can occur into the pericardial space. In accordancewith various embodiments, a catheter includes one or more electrodes, atleast one of which is used to make impedance measurements as describedabove to detect bleeding such as pericardial effusion. In anotherembodiment of this invention the tip of the catheter or electrode may belocated on any guide wire used during coronary intervention (a wire overwhich a coronary stent or angioplasty apparatus may be advanced isalways utilized during such procedures). In this embodiment, the guidewire is or contains an electrode. In such a situation the impedancebetween the tip of the wire and any second electrode as describedelsewhere (such as a skin patch electrode) can be utilized. In anotherembodiment a distal and proximal electrode (relative to the location ofcoronary blockage which is to be angioplastied or stented) within thesame wire may be used to assess progression of clot formation orperforation and effusion.

FIG. 8 illustrates an embodiment of an impedance measuring apparatus 150usable to measure impedance and detect bleeding. Any of the attributesdescribed below for impedance measuring apparatus 150 can apply toimpedance measuring apparatus 35 of FIG. 6 as well. The impedancemeasuring apparatus 150 comprises a processor 152, a detector 153, asignal generator 154, an output device 156 and storage 158. The storage158 comprises volatile memory (e.g., random access memory), non-volatilestorage (e.g., read only memory, hard disk drive, Flash storage, etc.),or combinations thereof. The storage 158 comprises an application 159usable to perform impedance measurements and detect bleeding asdescribed herein and calibration software 162. Both applications 159 and162 are executed by processor 152. Storage 158 is also used to store oneor more impedance thresholds 160. The impedance measuring apparatus 150comprises logic which includes any combination or all of the processor152, signal generator 154, and storage 158 (and associated applicationsand thresholds stored thereon).

Electrodes 172 are provided on a catheter 170 and electrically coupledto the signal generator 154. One or more additional electrodes 174 mayalso be provided and coupled to signal generator 154. Under control ofthe processor 152 (via execution of application 159), the signalgenerator 154 selects one pair of electrodes 172, 174, applies a knowncurrent to one of the electrodes in the selected pair and receives thecurrent via the electrode. The detector 153 determines the resultingvoltage across a selected pair of electrodes, which may be the same pairor a different pair of electrodes from that pair used to apply thevoltage, and provides the voltage measurement to the processor 152. Thedetector 153 may comprise an analog-to-digital converter to convert thevoltage measurement to digital form for the processor. Both the currentand voltage values are provided to the processor which then computes theimpedance (ratio of voltage to current), or conduction time and comparesthe computed impedance or conduction time to a corresponding thresholdto determine if bleeding has occurred. A pair of electrodes can beselected coupling two of the electrodes 172, 174 to the signal generator(via a switching device). The signal generator can select two electrodesfrom among electrodes 172 on the catheter, two electrodes from amongelectrodes 174, or one electrode each from electrode sets 172 and 174.

If two electrodes 172 are selected on the catheter 170, the impedancemeasuring apparatus 150 can detect a blood clot within the catheter bymeasuring the impedance between the two catheter electrodes. The same istrue with respect to the embodiment of FIG. 1. The sheath 12, in someembodiments, comprises more than one electrode 20. The impedancemeasuring apparatus 35 measures the impedance between the electrodes onthe sheath to detect blood clots that may form within the sheath.

The catheter 170 can be inserted into any of a variety of veins orarteries. In one embodiment, the catheter 170 is inserted into thefemoral artery (for detection, for example, of retroperitonealeffusion), the heart or coronary vasculature such as the coronary sinus(for detection of pericardial effusion), or other blood vessels oranatomic structures. The coronary sinus is an epicardial vein throughwhich venous drainage of coronary circulation occurs. It is on theinferior surface of the left atrium. More distally this structure turnsinto the great cardiac vein or any of its other tributaries.

The electrodes 174 may be located at any of variety of sites. Anelectrode 174, for example, may be located on the person's esophagus, onthe person's skin, or on the person's heart. Moreover, impedance can bemeasured for detecting bleeding between, for example, the coronary sinusand skin, coronary sinus and esophagus, skin and skin (e.g., patient'sfront and back), heart and coronary sinus, heart and esophagus, twosites on the same catheter, two sites on the same sheath, two sites onthe same vein and femoral artery to skin.

As explained herein, more than two electrodes can be used for measuringimpedance. Impedance can be measured between any pair of electrodes andsuch an impedance measurement represents a vector. For example, in athree-electrode system (first, second, and third electrodes), there arethree possible impedance vectors including the impedance between thefirst and second electrodes, the impedance between the first and thirdelectrodes, and the impedance between the second and third electrodes.The number of vectors increases disproportionately with increasingnumbers of electrodes. The physical location of the various electrodesmay be useful to detect bleeding in different locations. For example,bleeding may occur between the first and second electrodes, but thefluid (e.g., blood) may not be present between the second and thirdelectrodes. Thus, in this example, the impedance vector associated withthe first and second electrodes may be indicative of the bleed, but notso the impedance vector associated with the second and third electrodesor possibly the first and third electrodes. Moreover, more than twoelectrodes provides an enhanced ability to detect bleeding in differentlocations than might be possible in a two-electrode only system.

In some embodiments, the computed impedance may be resistance while inother embodiments, the computed impedance is complex having bothamplitude and phase components. In other embodiments the computedvariable is conduction velocity. Further, the impedance measuringapparatus 150 (or impedance measuring apparatus 35 in FIG. 6) determinesand stores an impedance threshold for each impedance vector. Two or moreof the various impedance thresholds may be the same or the impedancethresholds may all be different. Each impedance threshold may be anamplitude only value (resistance) or, in the case of complex impedance,comprise an amplitude value and a phase value.

FIG. 9 illustrates the thresholds 160 as a table comprising one or morevectors A, B, C, etc. Each vector represents a pair of electrodes. Foreach vector, there is an amplitude threshold value 166 and/or a phasethreshold value 168. In some embodiments, the impedance measuringapparatus detects the presence of bleeding if either of the amplitude orphase of the computed impedance for a given vector exceeds itscorresponding amplitude or phase value. In other embodiments, theimpedance measuring apparatus detects a bleed only if both the computedamplitude and phase exceed their corresponding threshold counterparts.The threshold counterparts may have been derived in a variety of waysone of which may be baseline measurements at the beginning of theprocedure for each individual patient as explained below.

FIG. 10 illustrates a method 200 for calibrating the impedance measuringapparatus (35 or 150) for the various thresholds. In some embodiments,the impedance measuring apparatus comprises a calibration mode that canbe initiated by a user of the impedance measuring apparatus (e.g., bypressing a button). The processor of the impedance measuring apparatusexecutes the calibration software 162 (impedance measuring apparatus 35may also have similar software to be executed by a processor). FIG. 10is a method performed by the processor upon executing the calibrationsoftware 162. The calibration mode is performed preferably before themedical procedure [e.g., coronary angiography (after the wire has beenplaced through the blockage but before angioplasty) or electrophysiologystudy (after catheters have been placed in the coronary sinus but beforedelivery of radiofrequency ablation)] begins.

The calibration mode begins at 202. A pair of electrodes is selected at204 and at 206 and 208, an impedance measurement is taken and thecomputed impedance is recorded (e.g., stored in storage 158) (asamplitude and/or phase values). Preferably, the impedance measurementfor a selected pair of electrodes is taken over the course of severalbreaths by the patient. The impedance computed for the selectedimpedance vector will vary during a respiratory cycle. By taking theimpedance measurement over the course of several breaths (e.g., 10seconds), the impedance measuring apparatus can account for the normalvariations in impedance. The threshold (amplitude or phase) may becomputed as an average during the recording period or may be set as thepeak value detected (or a value slightly higher (e.g., 5% higher) thanthe peak). At 210, the impedance measuring apparatus determines whetherthere is an additional impedance vector for which a threshold is to bedetermined. If there is, control loops back to step 204 at which such anelectrode pair is selected. If not more electrode pairs are to beselected, than the calibration mode stops at 212. This calibrationprocess may take several minutes. The same calibration variables may bemeasured for conduction velocities.

Once the calibration process is completed, the medical procedure (whichmight result in bleeding or clot formation) can begin. Any bleeding willbe detected a change in impedance above deviating from an impedancethreshold (e.g., an increase above the threshold or decrease below thethreshold).

The impedance measuring techniques described herein to detect bleedingare also usable to detect a hemothorax. In this application, electrodelocations would include the anterior chest and posterior chest walls,the esophagus at the level near the heart, the trachea, as well asnumerous intravascular and intra-cardiac and intra-coronary locations.The electrodes may be on catheters or wires.

With regards to conduction velocity, the logic (e.g., that contained inthe measuring devices described herein) assesses the conduction timebetween the onset of the electrical impulse in the first (transmitting)electrode and second (receiving) electrode. These electrodes areidentical to the electrodes described in embodiments of this invention.The electrical output is in the same range with regards to frequency andamplitude. The measured variable, however, is the difference (delta) intime (usually milliseconds) between onset of stimulus (electricaloutput) in the transmitting electrode and sensing of that impulse(electrical sensing) in the receiving electrode. Conduction velocity isheterogeneous with variations in tissue characteristic. As fluiddevelops, the conduction velocity between the transmitting and receivingelectrode will also change. This will be noted as a deviation from abaseline values (similar to the impedance values/thresholds describedherein). An alert will then be issued. The various embodiments ofapparatus and methods described above can also be used to measureconduction velocity and use conduction velocity to determine thickeningof the heart and the presence of fluid bleeding.

In accordance with some embodiments, the sheath 12 includes a wirelesstransceiver that is able to wireless transmit impedance values orimpedance-related values to an external apparatus rather than via awired connection as shown in FIG. 6. The embodiment of introducer 240 inFIG. 11 is similar in some ways to introducer 10 of Figure. Introducer240 includes sheath 242 which includes multiple electrodes 20 a-20 d aswell a hub 245. Hub 245 includes an impedance assessment unit 248.

As will be explained below, the impedance assessment unit 248 connectsto the electrodes via conductors 17 and is used during an impedancemeasurement. The impedance assessment unit may include a power source.In one embodiment, the impedance assessment unit sets a predeterminedcurrent or voltage for one pair of electrodes and measures the resultingvoltage or current from another electrode pair. The impedance assessmentunit may also include a wireless transmitter to transmit the measuredvoltage/current to the external apparatus which in turn computesimpedance based on the received, measured voltage/current and a priorknowledge of the predetermined current/voltage set by the impedanceassessment unit 248. Alternatively, the impedance assessment unit 248may also wirelessly transmit the current/voltage it set to the externalapparatus. Further still, the impedance assessment unit 248 may itselfcompute the impedance value and wirelessly transmit the computedimpedance value to the external apparatus. These and other embodimentsare discussed below.

FIG. 12 shows a block diagram of the impedance assessment unit 248. Asshown in the example of FIG. 12, the impedance assessment unit 248includes a power source 259, a controller 250, a wireless transceiver252, storage 254, a source unit 256, an alarm 257, and a measurementunit 258.

The power source 249 may comprise a battery (disposable orrechargeable), a charged capacitor, a wireless power receiver, or othersources of electrical power. The power source 249 provides electricalpower to the controller 250, wireless transceiver 252, storage 254 andsource unit 256.

The controller 250 executes software 260 provided on storage 254. Thecontroller 250, upon executing software 260, provides the impedanceassessment unit 248 with some or all of the functionality describedherein. The storage 254 may comprise volatile storage (e.g., randomaccess memory), non-volatile storage (e.g., flash storage, read onlymemory, etc.), or combinations of both volatile and non-volatilestorage. Data 262 consumed or produced by the software can also bestored on storage 254. For example, measured current or voltage values,computed impedance values, etc. can be stored on storage 254 pendingwireless transmission through the wireless transceiver 252 to anexternal apparatus.

The wireless transceiver may be implemented in accordance with anysuitable wireless protocol such as BLUETOOTH, WiFi, etc. The transceivermay be capable of transmitting only, or may be capable of transmittingand receiving. The controller 250 causes the wireless transceiver totransmit values indicative of impedance (current, voltage) or impedancevalues themselves. The transceiver 252 may be a bi-directional device topermit outgoing transmissions of data, as well as receive incomingcommands from an external apparatus. For example, an external apparatusmay send a command to the controller 250 via the wireless transceiver252 to command the impedance assessment unit 248 to initiate a processby which impedance is determined, or to transmit previously stored data(e.g., current, voltage, and/or impedance).

The source unit 256 receives power from the power source 249 andgenerates a current or voltage under control by the controller 250. Thesource unit 256 may generate a predetermined current or voltage, and isbroadly referred to as a source unit to indicate either or bothpossibilities. The source unit 256 is connected to a pair of electrodes(electrodes 20 a and 20 d in the example of FIG. 12), As a currentsource, the source unit 256 injects a current through one of theelectrodes 20 a,d and receives the return current through the other ofthe electrodes 20 a,d.

The measurement unit 258 measures the resulting voltage or current. Thatis, if the source unit 256 injects a predetermined current into thepatient, the measurement unit 258 measures the resulting voltage. If thesource unit 256 imposes a predetermined voltage across electrodes 20a,d, the measurement unit 258 measures the resulting current. In eithercase, the measurement unit 258 provides the measured electricalparameter to the controller 250.

The controller 250 thus knows the magnitude of the predetermined currentor voltage generated by the source unit 256 and the magnitude of themeasured voltage or current from the measurement unit 258. As such, thecontroller 250 can compute impedance, and do so as the ratio of voltageto current and transmit the computed impedance to the externalapparatus. However, as noted above, the controller 250 may not computeimpedance and instead transmit the measured electrical parameter(voltage or current) to the external apparatus for the externalapparatus to compute impedance. The external apparatus may or may notknow what predetermined current or voltage was set by the source unit256. If the external apparatus does know the magnitude of the sourceunit's current/voltage, that value need not be (but of course can be)transmitted to the external apparatus. If the external apparatus is notaware of the source unit's current/voltage magnitude, the controller 250preferably transmits both the measured voltage/current from themeasurement unit 258 and the source unit's predeterminedcurrent/voltage.

FIG. 13 illustrates an application of the use of the impedanceassessment unit 248. Sheath 242 containing impedance assessment unit 248is inserted into a patient's blood vessel as shown and a wirelesscommunication link 257 is established to an external apparatus 235. Theexternal apparatus 235 may contain a corresponding wireless transceiver236 as well as logic 238. The external apparatus may be computer(desktop, laptop, notebook, etc.), a smart phone, or any other type ofdevice capable wirelessly interacting with the impedance assessment unit248 of sheath 242. In some embodiments, the external apparatus is, or isbuilt into, a bedside monitor.

Regardless of whether the impedance assessment unit 248 computesimpedance or transmits the necessary data for the external apparatus tocompute the impedance, the computed impedance may be resistance based onDC current/voltage. In other embodiments, AC current/voltage is used andcomplex impedance is computed as a magnitude and a phase. ACcurrents/voltages have an associated frequency and impedancemeasurements can be made at any one or more of multiple differentfrequencies. All references to an impedance measurement being madeencompass any of the variations described herein as performed by thecombination of the impedance assessment unit and an external apparatus.

Impedance measurements made at certain frequencies may provide moreuseful information than at other frequencies. At certain frequencies, itmay be difficult to detect a bleed, where as other frequencies, bleeddetection is easier. Further, the particular frequenc(ies) useful todetect a bleed may vary from patient to patient. Accordingly, acalibration is performed at the beginning of a procedure using a sheathas described above. The calibration may entail performing multipleimpedance measurements at various frequencies. In some implementations,the range of acceptable frequencies is from 1000 Hz to 200 KHz, althougha different frequency range may be acceptable as well. Within thefrequency range multiple discrete frequencies are chosen to make theimpedance measurement. For example, 10 KHz may be chosen as well as 1000Hz, and 100 KHz.

The source unit 256 may be capable of injecting an AC current (orgenerating an AC voltage) at various frequencies as commanded by thecontroller 250. The controller 250 preferably is configured (e.g., byway of software 260) to initiate multiple impedance measurements atvarious frequencies during the calibration process. Each measuredelectrical parameter (e.g., voltage) may be stored in data 262 instorage 254 and mapped to the frequency of the source signal (e.g.,current) that caused the measured voltage to occur. Thus, multiple ACvoltages (or current) may be stored in storage 254, one voltage (orcurrent) corresponding to each AC current (or voltage) frequency. Themeasured parameters may be kept in storage 254 and/or wirelesslytransmitted to the external apparatus 235.

The calibration process may be initiated in any suitable manner. Forexample, a wireless command to initiate the calibration process may betransmitted from the external apparatus 235 to the impedance assessmentunit 248. Alternatively, impedance assessment unit 248 may have a userinput control (e.g., a button, switch, etc.) that a user can activate toinitiate the calibration process. Further still and in the case in whichthe power source is a battery, an electrically insulative strip mayprevent at least one of the battery's contacts from connecting the tothe rest of the impedance assessment unit 248 circuitry. Removal of thestrip may cause the controller 250 to initialize and start thecalibration process.

Then, at predetermined time periods (e.g., once per minute) aftercalibration, the controller 250 initiates additional impedancemeasurements to be made. At the expiration of each such time period, thecontroller 250 may also causes multiple impedance measurements to beinitiated at the same frequencies used during the calibration process.After computing the impedance values at the various frequencies (whetherthe impedance assessment unit or the external apparatus makes thecomputation as explained above), a comparison is made between each suchimpedance value and a previously computed impedance value. Thepreviously computed impedance value may be the impedance value computedduring calibration or any other previously computed impedance values. Adetermination is made as to whether the difference, as an absolutevalue, between the impedance value and the previously computed impedancevalue (e.g., calibration impedance value) is greater than apredetermined threshold. An impedance difference greater than thethreshold is an indicator of a bleed. Another way to make the comparisonis compute a ratio of the current impedance value to the previouslycomputed impedance value and then compare the ratio to a predeterminedrange. A ratio being outside the range is an indicator of a bleed.Bleeds may be easier to detect at certain frequencies rather than othersfor certain patients and thus the probability is higher that an actualbleed will be detected if multiple frequencies are used.

The process of taking impedance measurements and comparing to a previousimpedance value (e.g., calibration impedance values) is repeated at theexpiration of each subsequent time period. Additionally oralternatively, the impedance assessment unit 248 may be triggeredmanually to initiate an impedance measurement. The user can activate theuser control noted above, if such a user control is provided, or theexternal apparatus 235 may wirelessly transmit a command to cause thecontroller 250 to initiate a new impedance measurement.

Referring again to FIG. 12, in embodiments in which the impedanceassessment unit 248 computes impedance, the controller 250 may activatehe alarm 257 if a potential bleed is detected. The alarm may be a visualindicator such as a light emitting diode (LED), an audible indicatorsuch as a piezo-electric device, or both. While the embodiments of theinvention have been shown and described, modifications thereof can bemade by one skilled in the art without departing from the spirit andteachings of the invention. The embodiments described and the examplesprovided herein are exemplary only, and are not intended to be limiting.Many variations and modifications of the invention disclosed herein arepossible and are within the scope of the invention. Accordingly, thescope of protection is not limited by the description set out above, butis only limited by the claims which follow, that scope including allequivalents of the subject matter of the claims.

The discussion of a reference in the Background Information is not anadmission that it is prior art to the present invention, especially anyreference that may have a publication date after the priority date ofthis application. The disclosures of all patents, patent applications,and publications cited herein are hereby incorporated herein byreference in their entirety, to the extent that they provide exemplary,procedural, or other details supplementary to those set forth herein.

1. An introducer, comprising: a sheath for introducing a catheter into ablood vessel at an insertion site; a plurality of electrodes on thesheath; and an impedance assessment unit connected to said electrodes,said impedance assessment unit includes a power source and a wirelesstransceiver and is configured to: inject one of a predetermined currentor voltage across a first pair of electrodes and to measure the other ofthe current or voltage across a second pair of electrodes; and performat least one: wirelessly transmit current and voltage values to anexternal apparatus for detection of a bleed, and compute an impedancebased on the current and voltage and wirelessly transmit the computedimpedance to the external apparatus for detection of the bleed.
 2. Theintroducer of claim 1 wherein the impedance assessment unit isconfigured to serially inject the predetermined current or voltage atmultiple predetermined frequencies.
 3. The introducer of claim 1 whereinthe wireless transceiver in the impedance assessment unit is abi-directional wireless transceiver.
 4. The introducer of claim 3wherein the impedance assessment unit is configured to receive a commandvia the wireless transceiver to initiate injection of the predeterminedcurrent or voltage.
 5. The introducer of claim 3 wherein the impedanceassessment unit is configured to receive a command via the wirelesstransceiver to program an amplitude or frequency of the current orvoltage.
 6. The introducer of claim 1 wherein the impedance assessmentunit is configured to compute multiple impedance values and average themultiple impedance values together.
 7. The introducer of claim 1 whereinthe impedance assessment unit is configured to compute multipleimpedance values and compare the multiple impedance values to apreviously computed impedance value.
 8. The introducer of claim 1wherein the impedance assessment unit is configured to compute multipleimpedance values and compute a time rate of change of the computedimpedance values relative to a previously computed impedance value. 9.An apparatus, comprising: a guide wire configured to be inserted withina blood vessel at an insertion point and configured to guide anotherdevice to the insertion point; a first electrode provided on the guidewire; a second electrode; and a measuring device to which the first andsecond electrodes are coupled, said measuring device detects a bleed bymeasuring the impedance or conduction velocity between the firstelectrode on the guide wire and the second electrode.
 10. The apparatusof claim 9, wherein the measuring device detects the bleed by comparingthe impedance or conduction velocity to a threshold.
 11. The apparatusof claim 9 wherein the second electrode is on the guide wire.
 12. Theapparatus of claim 9, wherein the second electrode is disposed externalto the blood vessel.
 13. The apparatus of claim 12, wherein the secondelectrode is a skin electrode configured to be placed on an outer skinof a patient.
 14. The apparatus of claim 9, further comprising a thirdelectrode provided on the guide wire, wherein the third electrode iscoupled to the measuring device, and wherein the measuring device isconfigured to detect a bleed by measuring the impedance or conductionvelocity between at least two of the first electrode, the secondelectrode, and the third electrode.
 15. An apparatus, comprising: anintroducer usable to insert a catheter into a blood vessel, saidintroducer comprising a hollow sheathe to receive the catheter wheninserting the catheter into the blood vessel; a first electrode providedon the sheathe; a second electrode; and a measuring device to which thefirst and second electrodes are coupled, the measuring device to detecta blood clot by measuring the impedance or conduction velocity betweenthe first electrode on the sheathe and the second electrode.
 16. Theapparatus of claim 15, wherein the sheath comprises a tubular member andthe first electrode is provided on a surface of the tubular member. 17.The apparatus of claim 16, wherein the measuring device is to detect ablood clot within the tubular member by measuring the impedance orconduction velocity between the first electrode and the secondelectrode.
 18. The apparatus of claim 15, wherein the second electrodeis provided on the sheathe.
 19. The apparatus of claim 15, wherein themeasuring device is to detect a blood clot by comparing the impedance orconduction velocity to a threshold.